The physiological meaning of excretion is to expel waste from the body, to isolate and discharge waste matter generated during metabolism. This is achieved by the body's ability to rid itself of excess fluid by urination and by defecation, eliminating solid waste after the body has used the nutrients needed from the food taken in.
The body needs oxygen, water and nourishment in the form of food in order to survive. However, there are by - products that are produced during the metabolic processes that need to be excreted to prevent the body becoming toxic.
There are many processes of excretion that the human body implements to maintain its equilibrium. Waste products that need to be excreted come from the food that we eat and drink, air that we breathe and when the body becomes overheated it needs to be able to cool down. This heat is excreted so to speak, via the skin through sweating.
The air that we breathe contains oxygen and the lungs process this oxygen and distribute it throughout the body with the help of the circulatory system or through the blood. The by - product that forms after the oxygen has been taken up by all the cells in the body is called carbon dioxide and needs to be eliminated through the lungs. This is accomplished when the lungs exhale.
The kidneys process the fluid in the body and filter out the excess fluid as urine which contains unnecessary chemicals, such as those that come about through taking for example drugs and stimulants like alcohol, caffeine. These substances have a diuretic effect on the body.
The colon or large intestine processes the waste matter from the food we have eaten. This is fecal matter. After nutrients from the food have been absorbed in the small intestine, anything left over that has no nutritional value such as fibre, will then be evacuated from the body via the anus.
Heat and fluid are excreted through the body’s surface area, the skin. When the body’s temperature needs cooling down signals are sent via the pituitary gland to the blood vessels to dilate. This results in heat being lost through the pores on the skins surface and water that contains waste products being lost through the sweat glands. The main sweat glands are found in the armpits,or axilla. The body also sweats during illness if there is a fever. Another reason for sweating is if the body is under stress. This is known as the fight or flight response.